fold

fold1
/ fōld/
•
v. [tr.]
1.
bend (something flexible and relatively flat) over on itself so that one part of it covers another:
she folded all her clothes and packed all her bags. ∎
(fold something in/into)
mix an ingredient gently with (another ingredient), esp. by lifting a mixture with a spoon so as to enclose it without stirring or beating:
fold the egg whites into the chocolate mixture. ∎ [intr.]
(of a piece of furniture or equipment) be able to be bent or rearranged into a flatter or more compact shape, typically in order to make it easier to store or carry:
the deck chair folds flat |
[as adj.] (folding)
a folding chair. ∎
bend or rearrange (a piece of furniture or equipment) in such a way:
he folded up his tripod. ∎ [intr.] (fold out)
be able to be opened out; unfold:
the sofa folds out. ∎
(of a bird) collapse (its wings) and lay them flat against its body:
the crow folded its wings to a sharp angle and dive-bombed the vulture. ∎
(often be folded) Geol.
cause (rock strata) to undergo bending or curvature:
[as n.] (folding)
a more active period of igneous activity caused intense folding.2.
cover or wrap something in (a soft or flexible material):
a plastic bag was folded around the book. ∎
hold or clasp (someone) closely in one's arms with passion or deep affection:
Bob folded her in his arms and kissed her.3.
[intr.] inf.
(of an enterprise or organization) cease operating as a result of financial problems or a lack of support:
the club folded earlier this year. ∎
(esp. of a sports player or team) suddenly stop performing well or effectively:
he folded in the second round. ∎
(of a poker player) drop out of a hand:
an unerring knack for knowing when to fold and when to stay in.•
n.
1.
(usu. folds)
a form or shape produced by the gentle draping of a loose, full garment or piece of cloth:
the fabric fell in soft folds. ∎
an area of skin that sags or hangs loosely.
∎ chiefly Brit.
an undulation or gentle curve of the ground; a slight hill or hollow:
the house lay in a fold of the hills. ∎ Geol.
a bend or curvature of strata.
2.
a line or crease produced in paper or cloth as the result of folding it. ∎
a piece of paper or cloth that has been folded:
a fold of paper slipped out of the diary.PHRASES:fold one's arms
bring one's arms together and cross them over one's chest.fold one's hands
bring or hold one's hands together.DERIVATIVES:fold·a·ble
adj.fold2 •
n.
a pen or enclosure in a field where livestock, esp. sheep, can be kept. ∎ (the fold)
a group or community, esp. when perceived as the locus of a particular set of aims and values:
he's performing a ritual to be accepted into the fold.•
v. [tr.]
shut (livestock) in a fold.

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fold

The Columbia Encyclopedia, 6th ed.

Copyright The Columbia University Press

fold, in geology, bent or deformed arrangement of stratified rocks. These rocks may be of sedimentary or volcanic origin. Although stratified rocks are normally deposited on the earth's surface in horizontal layers (see stratification), they are often found inclined or curved upward or downward. Arches, or upfolds, in stratified rock are called anticlines; depressions or downfolds, synclines. A third type of fold, the monocline, is a steplike structure sloping in one direction only. It is more correctly called a flexure and generally passes at depth into a fracture called a fault. An imaginary line drawn along the crest of an anticline or the trough of a syncline is its axis; the two sides curving away from the axis are the limbs. If both limbs, dipping in opposite directions, make the same angle with the horizontal, and if an imaginary axial plane passed through the axis and the center of the fold is vertical and divides the fold into two equal halves, the fold is symmetrical; if the limbs make unequal angles, and if the axial plane is inclined and does not bisect the fold, the fold is asymmetric. If one limb lies partly under the other, and the axial plane is inclined, the fold is overturned; if one limb lies almost completely under the other, and the axial plane is almost horizontal, the fold is recumbent. The axis of a fold cannot be indefinitely extended parallel to the horizontal, but plunges or emerges as the fold tapers off to a plane. Certain domes are very short anticlines with axes plunging at both ends, while some basins, similarly, are synclinal structures. Folds are commonly formed at some distance below the surface, but complete folds or portions of folds are exposed by erosion. Anticlines frequently have their crests eroded, till only the worn-down stumps of the two limbs remain. In a similar manner synclines may be eroded so that only the edges of the limbs project above the surface. The ridge crests of the Appalachian Mts. are eroded limbs of folds. The nature of the original fold can generally be determined from the arrangement of the outcrops, or exposed portions; thus, two outcrops dipping toward each other mark a syncline, and two outcrops dipping away from each other, an anticline. Folds on a grand scale, extending, for example, most of the length of a continent, are known as geosynclines and geanticlines. The immediate cause of folding is generally conceded to be the horizontal compression of the earth's surface, anticlines being squeezed up by this compression and synclines formed between anticlines. The problem of the ultimate cause of fold formation is similar to that of fault formation, both being earth movements involved in mountain building and plate tectonics. Porous and permeable rocks of anticlines often contain oil and gas reservoirs. Organic remains of late Paleozoic tree fern swamps were converted to anthracite coal during the folding of the Appalachian Mts.

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fold

fold1. A bend in rock strata or in any planar feature. The feature (e.g. bedding, cleavage, or layering) is deflected sideways and the amount and direction of dip is altered. Four principal regimes are responsible for folding: layer-parallel or lateral compression; differential vertical subsidence; differential shearing; and thrusting. In a simple anticline—syncline fold pair, an individual fold consists of a curved hinge zone and two planar limbs. An imaginary fold axis lies parallel to the hinge zone (line) and marks the intersection of the axial plane (or surface) with this zone. This basic geometric form gives rise to many fold profiles, including parallel, similar, concentric, open, and isoclinal fold types. To define the attitude of a fold accurately, the orientation of both the hinge line and the axial plane have to be measured. Varying orientations of the hinge line and axial plane may give rise to widely differing fold attitudes, thus vertical, upright and inclined (horizontal and plunging, see PLUNGE), and reclined and recumbent forms may be described.

2. In seismic reflection sampling, the number of offset distances which sample one common depth point. For example, if one CDP is sampled at 24 offset distances it is referred to as ‘24-fold’ coverage. The signals recorded for the CDP on each separate trace are then summed by stacking to improve the signal-to-noise ratio.

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fold

fold In geology, a bend in a layer of rock. An upfold is an anticline; a downfold a syncline. The line around which the rock is folded is termed the fold axis. The fold system may be symmetrical, asymmetrical, overturned or recumbent (with the axis of the fold horizontal). A single folding is a monocline.

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